The search for antiarrhythmic drugs among agents which do not depress cardiac contractility merits intensive work. We have demonstrated that prostaglandin E1 and E2 prevent ouabain cardiotoxicity in the cat and dog without decreasing the inotropic effect of ouabain. The present research will study other prostaglandins which may be effective in our arrhythmia model and will attempt to clarify their mechanism of action. The present work will attempt to define the most promising and antiarrhythmic compounds among the available prostaglandins and to document the optimum rated administration needed to provide an optimum antiarrhythmic effect.